1. Field of the Invention
The present invention generally relates to a probe used for an optical memory such as an optical disc, an optical card, an optical tape, or the like, to which information is recorded, from which information is reproduced, and from which information is erased, using light, and, in particular, to a near field optical probe which generates the optical near field and detects scattered light generated through the optical near field and a manufacturing method thereof.
2. Description of the Related Art
In an optical memory, which has been put to practical use, a laser spot, obtained from converging laser light to the diffraction limit, is caused to be incident on a recording medium. At this time, information is recorded on the recording medium as a result of thermal and magnetic modulation being performed on a recording layer of the recording medium. Further, by detecting the intensities of reflected light modulated by record bits, the information is reproduced. In such information recording means, the recording density of the recording medium is approximately determined by the laser wavelength. In order to cope with a recent increase in an information amount processed in various types of information apparatuses such as computers and so forth, a large-capacity memory which achieves a recording density which is obtained as a result of the diffraction limit being exceeded has been demanded. As a promised next-generation large-capacity memory such as that mentioned above, an optical memory on which information recording, reproducing and erasing are performed using the optical near field was proposed. Examples thereof will now be described.
(1) xe2x80x98Near Field Optics and Its Application to Optical Memory,xe2x80x99 a thesis journal of the Institute of Electronics, Information and Communication Engineers, C-I, Vol. J81-C-I, No. 3, Pages 119-126, March, 1998, proposes a device in which a two-dimensional aperture row is formed in a silicon substrate using a semiconductor-plane-process technique, and the optical near fields are generated on the apertures by light which has been incident on the top surface of the silicon substrate. Further, this literature suggests a possibility of integration with a photodetector array.
(2) Japanese Laid-Open Patent Application No. 9-198830 discloses that, in a high-density recording apparatus using the optical near field, in order to stably generate the optical near field in proximity to a recording medium, a high-density recording is performed using a slider in which a circular-cone-shape through hole having an aperture is provided.
Thus, the device in which the two-dimensional aperture row is formed in the silicon substrate using the semiconductor-plane-process technique, and the optical near fields are generated on the apertures by light which has been incident on the top surface of the silicon substrate, was proposed. When a photodetector is integrated into such a device, it is possible to miniaturize such a near field optical probe, and to improve efficiency in detection because it is possible that scattered light and so forth generated through the optical near field can be received in the proximity.
An object of the present invention is to provide a specific structure and a manufacturing method of a near field optical probe having an arrangement in which an aperture for generating the optical near field which was proposed and a semiconductor photodetector (photodiode: PD) are integrated so as to be combined.
Another object of the present invention is to provide a near field optical probe which can perform a light-detecting operation stably at high speed while generating the optical near field from an aperture.
Another object of the present invention is to provide a manufacturing method of a near field optical probe in which, when an arrangement in which a through hole is surrounded by a ring-shaped high-concentration impurity region along the direction of the through hole is produced, it is easy to form the high-concentration impurity region to a deep portion of the through hole.
Another object of the present invention is to simplify a manufacturing method of a near field optical probe in which a metal film for shading necessary for generation of the optical near field and a terminal which is a component of a photodetector are formed simultaneously.
In a near field optical probe, according to the present invention, a through hole having an aperture is provided in a semiconductor photodetector including at least a first-conductive-type high-concentration impurity layer, a first-conductive-type low-concentration impurity layer and a second-conductivity-type impurity-introduced region.
In this arrangement, by integration of the aperture for generating the optical near field and the semiconductor photodetector (photodiode: PD), which integration has been proposed in the related art, it is possible to miniaturize the near field optical probe and to remarkably improve detection of diffused light generated through the optical near field.
A method for manufacturing the above-described near field optical probe, according to another aspect of the present invention, in which probe the through hole having the aperture is provided in the semiconductor photodetector including at least the first-conductive-type high-concentration impurity layer, the first-conductive-type low-concentration impurity layer and the second-conductivity-type impurity-introduced region, comprises the steps of:
a) forming the second-conductive-type impurity-introduced region in the surface of the first-conductive-type low-concentration impurity layer of a semiconductor substrate having the first-conductive-type high-concentration impurity layer and first-conductive-type low-concentration impurity layer;
b) forming the through hole, which passes through the first-conductive-type high-concentration impurity layer and first-conductive-type low-concentration impurity layer, from the side of the first-conductive-type high-concentration impurity layer, after the step a); and
c) forming the aperture in the second-conductive-type impurity-introduced region, after the step b).
In this method, it is possible to cope with various variations in conditions at the time of forming the through hole and manufacture the above-described near field optical probe.
A method for manufacturing the above-described near field optical probe, according to another aspect of the present invention, in which probe the through hole having the aperture is provided in the semiconductor photodetector including at least the first-conductive-type high-concentration impurity layer, first-conductive-type low-concentration impurity layer and second-conductivity-type impurity-introduced region, comprises the steps of:
a) forming the through hole, which passes through the first-conductive-type high-concentration impurity layer and first-conductive-type low-concentration impurity layer, from the side of the first-conductive-type high-concentration impurity layer; and
b) forming the second-conductive-type impurity-introduced region in the surface of the first-conductive-type low-concentration impurity layer of a semiconductor substrate having the first-conductive-type high-concentration impurity layer and first-conductive-type low-concentration impurity layer, after the step a).
In this method, it is possible to prevent conditions from being complicated due to differences in conductive-type at the time of forming the through hole, and manufacture the near field optical probe stably.
In a near field optical probe, according to another aspect of the present invention, in which probe a through hole having an aperture is provided in a semiconductor photodetector including at least a first-conductive-type high-concentration impurity layer, a first-conductive-type low-concentration impurity layer and a second-conductivity-type impurity-introduced region,
the second-conductive-type impurity-introduced region is provided separately from the aperture.
In this arrangement, because the second-conductive-type impurity-introduced region is provided separately from the aperture, it is possible to prevent a path of an electric current extending from the second-conductive-type impurity-introduced region and passing directly through the surface of the through hole from developing, and, thereby, it is possible to achieve a stable operation of the semiconductor photodetector.
In a near field optical probe, according to another aspect of the present invention, in probe which a through hole having an aperture is provided in a semiconductor photodetector including at least a first-conductive-type high-concentration impurity layer, a first-conductive-type low-concentration impurity layer and a second-conductivity-type impurity-introduced region,
the through hole is surrounded by a ring-shaped first-conductive-type impurity region provided along the direction of the through hole in the first-conductive-type low-concentration impurity layer.
In this arrangement, because the through hole is surrounded by the ring-shaped first-conductive-type impurity region provided along the direction of the through hole in the first-conductive-type low-concentration impurity layer, this ring-shaped first-conductive-type impurity region functions as a preventing layer such that, although a depletion layer extending from the second-conductive-type impurity-introduced region along the direction of the surface of the through hole grows along the surface of the through hole at the time of reverse bias or zero bias, the growth of the depletion layer stops within a slight amount. Thereby, it is possible to prevent development or increase of a surface leakage current due to development of a channel along the through hole.
In the above-described near field optical probe, the ring-shaped first-conductive-type impurity-introduced region may be provided so as to be connected to the first-conductive-type high-concentration impurity layer.
Thereby, the ring-shaped first-conductive-type high-concentration impurity region has not only the above-described function of preventing growth of the channel, but also a function of a substrate-side high-concentration impurity layer of a so-called PIN-type PD. Thus, it is possible to optoelectrically transduce light received in the proximity of the aperture so as to effectively draw the light as an electric current. That is, it is possible to increase the efficiency of light detection in the proximity of the aperture.
In a near field optical probe, according to another aspect of the present invention, in which probe a through hole having an aperture is provided in a semiconductor photodetector including at least a first-conductive-type high-concentration impurity layer, a first-conductive-type low-concentration impurity layer and a second-conductivity-type impurity-introduced region,
a first-conductive-type high-concentration impurity-introduced region is provided at a portion spreading from and in the proximity of the surface of the first-conductive-type low-concentration impurity layer, has a plane shape containing the aperture and is separate from the second-conductive-type impurity-introduced region.
In this arrangement, it is possible to prevent a channel from extending from the second-conductive-type impurity-introduced region along the surface of the near field optical probe.
In the above-described near field optical probe, the through hole may be surrounded by a ring-shaped first-conductive-type high-concentration impurity region extending along the direction of the through hole in the first-conductive-type low-concentration impurity layer, and, also, the ring-shaped first-conductive-type high-concentration impurity region may be provided so as to be connected to the first-conductive-type high-concentration impurity-introduced region having the plane shape containing the aperture and formed separate from the second-conductive-type impurity-introduced region.
In this arrangement, it is possible to prevent a channel from extending from the second-conductive-type impurity-introduced region along the surface of the near field optical probe, and, also, along the surface of the through hole. Thereby, it is possible to positively achieve reduction in leakage current.
In the above-described near field optical probe, a dielectric film may be provided on the surface, of at least the first-conductive-type low-concentration impurity layer, of the through hole.
This dielectric film functions as a protective film for the surface of the semiconductor surface, and can prevent a leakage current from developing in the semiconductor photodetector due to defects, impurities or the like in interfaces. Further, in a case where a metal film is laminated, the dielectric film functions as an insulative film. Thereby, it is possible to prevent operation failure of the photodetector due to time-elapse deterioration or leakage, and to prevent a short circuit due to the lamination of the metal film.
A method for manufacturing the near field optical probe, according to another aspect of the present invention, comprises the step of impurity diffusion using an impurity in a gas phase, which step is performed when the ring-shaped first-conductive-type high-concentration impurity region extending along the direction of the through hole is formed.
In this method, even when the sectional shape of the through hole is a vertical shape or a relatively steep taper shape, it is possible to form the ring-shaped first-conductive-type high-concentration impurity region surrounding the through hole, because the impurity diffusion using the impurity in the gas phase is used.
In the above-described near field optical probe, metal films may be provided on the surface of the through hole and the surface of the first-conductive-type high-concentration impurity layer.
Thereby, the metal film provided on the through hole functions as a shading film for preventing light from penetrating the substrate when the light is incident on the through hole for the purpose of generation of the optical near field and a reflecting film for necessity from the optical near field generation principle or increase of the optical near field. Further, the metal film provided on the surface of the first-conductive-type high-concentration impurity layer functions as a conductive path to a circuit for light detection and so forth.
A method for manufacturing the near field optical probe, according to another aspect of the present invention, comprises the step of forming, at the same time, the metal film on the surface of the through hole and the metal film on the surface of the first-conductive-type high-concentration impurity layer.
In this method, it is possible to omit a process and to improve the manufacturing efficiency.
In a near field optical probe, according to another aspect of the present invention, in which probe a through hole having an aperture is provided in a substrate in which a semiconductor photodetector is formed,
a light-receiving region of the semiconductor photodetector is provided so as to be limited to the proximity of the aperture.
In this arrangement, because the light-receiving region of the semiconductor photodetector is provided so as to be limited to the proximity of the aperture, it is possible to prevent an increase in a CR time constant, and to achieve the near field optical probe which can operate at high speed.
In a near field optical probe, according to another aspect of the present invention, in which probe through holes having a plurality of apertures are provided in a substrate in which a semiconductor photodetector is formed,
a light-receiving region of the semiconductor photodetector is provided so as to be limited to the proximity of each of the plurality of apertures, and, also, a plurality of the light-receiving regions are electrically connected with each other.
In this arrangement, because the light-receiving region of the semiconductor photodetector is provided to be limited to the proximity of each of the plurality of apertures, and, also, the plurality of the light-receiving regions are electrically connected with each other, even in a case where the area of the near field optical probe formed as an array increases, it is possible to prevent an increase in a CR time constant, and to achieve the near field optical probe which can operate at high speed.
In a near field optical probe, according to another aspect of the present invention, in which probe a through hole having an aperture is provided in a substrate in which a semiconductor photodetector is formed,
a surface of a wiring layer which is connected to a light-receiving region of the photodetector does not project from an imaginary plane including the surface of the aperture.
In this arrangement, because the surface of the wiring layer which is connected to the light-receiving region of the photodetector does not project from the imaginary plane including the surface of the aperture, it is possible to achieve a near field optical probe, the aperture of which can be placed so close to an object that the distance therebetween is equal to or less than an amount on the order of tens of nm.
In a near field optical probe, according to another aspect of the present invention, in which probe a through hole having an aperture is provided in a substrate in which a semiconductor photodetector is formed,
a wiring layer which is electrically connected to a light-receiving region of the photodetector is provided along a through hole provided in the substrate.
In this arrangement, because the wiring layer which is electrically connected to the light-receiving region of the photodetector is provided along the through hole provided in the substrate, it is possible to achieve an arrangement in which, without adversely affecting the function of the near field optical probe, electrical connection to a wiring element on the rear surface from a wiring element of the photodetector on the side of the light-receiving surface can be made.